(1) Field of the Invention
The present invention relates to a rotor including a lead/lag abutment mechanism, and to an aircraft having such a rotor.
The invention thus lies in the technical field of rotorcraft rotors. More specifically, the invention lies in the field of abutments fitted to such a rotor to limit the lead/lag movement of the lift assemblies carried by the hub of the rotor.
(2) Description of Related Art
A rotorcraft usually has at least one rotor for providing the rotorcraft with at least part of its lift and possibly also with propulsion.
A rotor comprises a hub that is set into rotation by a mast. The hub then carries at least two lift assemblies. Consequently, each lift assembly is provided with a blade that is connected to the hub via at least one retention and mobility member. Each blade may in particular comprise a lift element fastened to a cuff or indeed a lift element having an incorporated cuff.
By way of example, a retention and mobility member includes a hinge referred to as a “spherical abutment”. Each spherical abutment may have one strength member fastened to the hub and another strength member fastened to a cuff, regardless of whether the cuff is or is not incorporated in a lift element.
The blades are thus substantially plane elongate elements that are carried by the hub. The blades are mounted on the hub by individual members for mounting the blades on the hub, which members include the retention and mobility members connecting the lift assemblies to the hub.
A hub may be a hub having two plates secured to a mast. By way of example, one of the strength members of a retention and mobility member is fastened to the two plates by a pin.
In another embodiment, the hub may comprise a single plate fastened to the mast, the plate being provided with radial arms including openings. A retention and mobility member is optionally positioned in each opening, being secured to the plate by one of its strength members. A cuff then extends on either side of the plate from the retention and mobility member to a lift element.
The mounting members are fitted respectively to each of the blades at their root ends in order to enable the blades to be maneuvered by an operator. By way of example, the ability of the blades to move relative to the hub makes it possible for a pilot of the rotorcraft in flight to cause the pitch of the blades to vary collectively or cyclically in order to influence the behavior of the rotorcraft in terms of its lift and/or its propulsion.
The freedom of the blades to move relative to the hub allows them to move with lead/lag movement, pitch movement, and flapping movement.
In order to control pitch, the cuff may also include a horn hinged to a pitch lever that is connected to a control device for controlling the pitch of the blade. Operating the control device causes the pitch lever to move in translation, which movement in translation serves to modify the pitch of the blade.
Under such conditions, the lead/lag movement of the blade can lead to an impact between the hub and the cuff of a blade, and in particular against its pitch lever.
Furthermore, certain rotors are fitted with inter-blade lead/lag adapters, each extending between two adjacent blades. For such rotors, the collective lead/lag mode is nevertheless not damped by the lead/lag adapters. Under such circumstances, a manufacturer may seek to protect the hub against the impacts that occur as a result of collective lead/lag movement of the lift assemblies, in particular during stages of starting and stopping the rotor, relating respectively to stages of acceleration and deceleration.
Document EP 0 340 095 describes a hub having bulges presenting lead/lag abutment surfaces facing abutment surfaces of the blades. The lead/lag abutment surfaces are slightly rounded with double curvature.
Also known are “sacrificial” metal abutments arranged on the arms of hubs carrying blades. Two metal abutments per blade are arranged on the hub to serve as abutments in the event of lead/lag movement of the blade in two opposite turning directions.
Each metal abutment is in the form of a clip fastened to the end of the arm so as to face a cuff.
Instead of impacting against the hub as a result of a lead/lag movement, a lift assembly can come into abutment against a lead/lag abutment.
Nevertheless, such a metal abutment can be difficult to put into place on a hub made of composite materials. A hub made of composite materials may present dimensional dispersions in manufacture relative to a theoretical definition. Under such circumstances, the real shape of a hub made of composite materials may make it difficult to arrange a metal lead/lag abutment that is dimensioned on the basis of the theoretical shape of the hub.
Furthermore, the end of the arm may be complex in shape, e.g. it may be a truncated cone. A metal abutment may be difficult to adapt to such a complex shape, with installation being even more difficult when there are dimensional dispersions due to fabrication of the hub.
Furthermore, the impact of a lift assembly against a metal abutment leads to a local force peak that runs the risk of locally delaminating a hub that is made of composite materials.
Documents U.S. Pat. Nos. 4,235,570 and 4,203,708 describe helicopter rotors, each having blades hinged to a hub via a retention and mobility member of the spherical abutment type.
Furthermore, each blade is connected to an arm of the hub by an actuator for limiting the lead/lag movement of a blade. Such movement is restricted to an angular range extending between a first position in which the actuator is fully retracted and a second position in which the actuator is fully extended.
Document U.S. Pat. No. 4,551,067 describes a rotor having retractable lead/lag abutments.
Document U.S. Pat. No. 4,297,079 does not lie in the technical field of rotorcraft rotors. Document U.S. Pat. No. 4,297,079 describes a marine propeller.
Also known are Documents U.S. Pat. No. 3,106,965 and EP 0 478 444.